Mutations identified in patients with MED have now been found in the genes encoding cartilage oligomeric matrix protein (COMP), matrilin-3 (MATN3), and type IX collagen (COL9A1, COL9A2, and COL9A3) for the autosomal dominant forms, while mutations in SLC26A2 cause autosomal recessive MED [Briggs and Chapman, 2002]. This evidence concerns the gene COL9A3 and multiple epiphyseal dysplasia.